1. Field of the Invention
The present invention relates to a carrier and a polishing apparatus capable of picking up, pressing, and releasing a wafer or other workpiece.
2. Description of the Related Art
FIG. 17 is a sectional view of a carrier of the related art.
A carrier 100 is comprised of a housing 101, a carrier base 103 attached to the bottom surface of the housing 101 and having a backing sheet 102 at its bottom surface, and a retainer ring 104 attached to the outer periphery of the bottom surface of the carrier base 103.
The carrier 100 is further formed with a plurality of air holes 106 passing through the backing sheet 102 and carrier base 103 and communicating with grooves 105 of the housing 101 at their upper ends, and an air exit/inlet communicating with the grooves 105.
Due to this, the wafer W may be picked up by making the insides of the air holes 106 a negative pressure state. At the time of polishing, the negative pressure state inside the air holes 106 is released and the wafer W polished while pressing the wafer W by the carrier base 103 against a polishing pad 111 of a rotating platen 110. Further, by supplying water at a predetermined pressure into the air holes 106, the polished wafer W can be released from the backing sheet 102.
In this carrier 100, however, since the back surface of the wafer W (top surface in FIG. 17) is pressed by a hard carrier base 103, that is, the so-called back side reference system is adopted, it is not possible to obtain a desired precision when flattening the front surface of a wafer W (bottom surface in FIG. 17).
Therefore, as shown in FIG. 18, a carrier adopting a so-called front side reference system has been devised.
A carrier 300 provides a ring-shaped projecting portion 302 at the outer peripheral portion of the bottom surface of a carrier base 301. By adhering a film 305 having a plurality of holes 305a to the bottom surface of the projecting portion 302, a pressure chamber 303 is defined. A retainer ring 304 is adhered by a double-sided adhesive tape 308 at the outer peripheral portion of the bottom surface of the film 305, that is, to a position corresponding to the projecting portion 302.
Due to this configuration, it is possible to pick up the wafer W by placing the inside of the pressure chamber 303 in a negative pressure state and, at the time of polishing, to return the inside of the pressure chamber 303 to the positive pressure state and polish the wafer W while pressing the wafer W against the polishing pad 111 of the rotating platen 110 by the air in the pressure chamber 303 through the film 305. Further, it is possible to supply water at a predetermined pressure into the pressure chamber 303 to release the polished wafer W from the film 305.
The carrier 300 shown in FIG. 18, however, had the following problem:
With this carrier 300, the film 305 would deform to match the shape of the back surface of the wafer W. Further, the entire surface of the wafer W was pressed by a uniform air pressure. Therefore, it was possible to polish the surface of the wafer W to a high precision.
Since the air in the pressure chamber 303 escaped to the outside from the holes 305a in the film 305 and then along the upper surface of the wafer W, however, the wafer W was contaminated, i.e., so-called leak contamination occurred. Further, the polishing solution entering between the retainer ring 304 and the wafer W was dried by the air escaping from the holes 305a resulting in abrasive becoming affixed on the inner peripheral surface of the retainer ring 304. Therefore, clumps of abrasive could peel off during polishing and scratch the wafer W.